Selenium geochemistry of paddy soils in Yangtze River Delta

Selenium (Se) content both in total and bioavailable forms were very low (25-35 and 9.5 micrograms/kg, respectively) in waterlogged paddy soils in the central Yangtze River Delta. This was due to changes in geochemistry and the inherent properties of the parent materials of these lowland paddy soils. The very low Se content (23 micrograms/kg) in the parent material resulted in low total Se content in the soil. The main chemical changes under long-term waterlogged conditions are depletion of molecular oxygen, decrease of redox potential, and reduction of Fe (III) to Fe (II) and SeO3(2-) to Se0. This led to low availability of Se in soils, and subsequently low Se content (29 micrograms/kg) in brown rice grain produced in this region. It has been suspected that low Se content in staple food might be one of the major reasons for a high infection rate of the intestine and stomach cancers and the higher death rate caused by these diseases in the region. Foliage spray of Na2SeO3 at early heading stage of rice plant growth improved the Se content of brown rice grain, hull, and straw, and would improve human and animal health.     

Actinide analysis of a depleted uranium penetrator from a 1999 target site in southern Serbia

Following the detection of 236U in depleted uranium (DU) ammunition used during the Balkans conflict in the 1990s, concern has been expressed about the possibility that other nuclides from the nuclear fuel cycle and, in particular, transuranium nuclides, might be present in this type of ammunition. In this paper, we report the results of uranium and plutonium analyses carried out on a depleted uranium penetrator recovered from a target site in southern Serbia. Our data show the depleted nature of the uranium and confirm the presence of trace amounts of plutonium in the penetrator. The activity concentration of (239+240)PU, at 45.4+/-0.7 Bq kg(-1), is the highest reported to date for any penetrator recovered from the Balkans. This concentration, however, is comparable to that expected to be present naturally in uranium ores and, from a radiological perspective, would only give rise to a very small increase in dose to exposed persons compared to that from the DU itself.     

Agronomic Water Mass Balance vs. Well Measurement for Assessing Ogallala Aquifer Depletion in the Texas Panhandle

The Ogallala Aquifer is depleting faster than it is being replenished. Interpretation of well data suggests that the water table in some counties is not declining, or not as much as might be expected in view of the amount of land being irrigated. As the Ogallala Aquifer in the Texas Panhandle receives almost no recharge, a possible explanation is that the current method of using well data for estimating the quantity of water remaining in the aquifer is underestimating water in storage. This study used an agronomic water mass balance approach to estimate how much water has been used for irrigation compared to amounts estimated by well data. The major finding was in counties where irrigation well capacities have declined significantly but irrigation is continuing, there is likely more water in storage than presently estimated, but the amounts of water being used for irrigation in those counties are greater than estimated changes of water in storage. The proposed hypothesis for this difference is there are mounds of water between wells that are not being accounted for and data are presented and discussed to support this conjecture.     

In vitro toxic effects of heavy metals on fungal growth and phosphate-solubilising abilities of isolates obtained from Phragmites australis rhizosphere

In this research, we evaluated the toxic effect of metal ions on mycelial growth and phosphate-solubilising activity of soil-borne micromycetes isolated from the Phragmites australis rhizosphere using Pikovskaya-agar plates supplemented with four metal concentrations. The diameter growth rate (DGR) decreased as the metal concentration rise for all tested fungi. Trichoderma atroviride had the fastest growth rate (1.48?cm²?day^?1) and was the least susceptible to Al³⁺, Cd²⁺, Cr³⁺, Cu²⁺ and Pb²⁺ with a median effective concentration (MEC₅₀) of 12.19, 0.48, 4.51, 11.44 and 50.05?mM, respectively. Aspergillus japonicus was the most tolerant to Co²⁺, Ni²⁺ and Zn²⁺, with MEC₅₀ values of 3.36, 1.095 and 2.34?mM, respectively. Penicillium italicum was the most tolerant to Cr6⁺ (MEC₅₀?=?0.677?mM). The ability to solubilise phosphate remained, despite the decrease in the DGR, and P. italicum and Penicillium dipodomyicola had the highest Phosphate Solubilisation Indexes (PSIs) at 1.97 and 2.12, respectively. In particular, P. italicum recorded the highest PSI of all the studied isolates at 0.62?mM Cr³⁺ (PSI?=?4.74). A. japonicus and T. atroviride were the most tolerant isolates to all tested metals, which suggests that these isolates are promising candidates for further study with regard to mycoremediation and biofertilisation of metal-polluted soils.     

根表铁膜的形成和添加硒对水稻吸收转运无机汞和甲基汞的影响

为了研究根表铁膜和硒对水稻吸收、转运不同形态的汞的影响,用Fe2+溶液诱导根表形成铁膜后,将水稻植株分别暴露于无机汞(Hg Cl2)、甲基汞(Me Hg Cl)、无机汞和亚硒酸钠(Hg Cl2+Na2Se O3)混合溶液、甲基汞和亚硒酸钠(Me Hg Cl+Na2Se O3)混合溶液的培养液中继续培养72 h。用DCB(dithionite-citrate-bicarbonate)提取根表铁膜,并用电感耦合等离子体质谱(ICP-MS)测定DCB溶液中Fe、Hg含量及水稻根、茎叶中Hg含量。结果表明:水稻根表铁膜对Me Hg Cl和Hg Cl2均有吸附,对Me Hg Cl的吸附作用高于Hg Cl2。根表铁膜的形成显著降低了汞暴露水稻根、茎叶中汞的含量;铁膜的形成也显著降低了Hg Cl2和Me Hg Cl从水稻根部到茎叶部分的转运效率。硒的存在可增加铁膜对Hg Cl2和Me Hg Cl的吸附,降低水稻对Hg Cl2和Me Hg Cl的吸收和转运。研究结果表明:根表铁膜和硒单独或联合作用能显著抑制水稻对无机汞和甲基汞的吸收和转运,进而可以减少汞在稻米中的蓄积。研究的开展对于提高汞污染区稻米的质量和保证粮食安全具有一定的现实意义。     

Stable isotopes identify an ontogenetic niche expansion in Antarctic krill (Euphausia superba) from the South Shetland Islands, Antarctica

Antarctic krill (Euphausia superba) occupy a key position in the Southern Ocean linking primary production to secondary consumers. While krill is a dominant grazer of phytoplankton, it also consumes heterotrophic prey and the relative importance of these two resources may differ with ontogeny. We used stable isotope analyses to evaluate body size-dependent trophic and habitat shifts in krill during the austral summer around the South Shetland Islands, Antarctica. We found evidence for an asymmetric, ontogenetic niche expansion with adults of both sexes having higher and more variable δ¹⁵N values but consistent δ¹³C values in comparison with juveniles. This result suggests that while phytoplankton likely remains an important life-long resource, krill in our study area expand their dietary niche to include higher trophic food sources as body size increases. The broader dietary niches observed in adults may help buffer them from recent climate-driven shifts in phytoplankton communities that negatively affect larval or juvenile krill that rely predominately on autotrophic resources.     

Contamination status of arsenic,lead, and cadmium of different wetland waters

The present investigation was conducted to determine the contamination status of arsenic (As), cadmium (Cd), and lead (Pb) in the wetland waters of Bhaluka in Bangladesh. Water samples were collected from 15 selected wetlands of Bhaluka region and analyzed using an atomic absorption spectrophotometer. Estimated results of three metals detected were As (7–80?µg?L^?1), Pb (0–86?µg?L^?1) and Cd (0–70?µg?L^?1) in water samples in all wetlands. The level of As in all investigated wetlands (93%) was higher than that of WHO recommended permissible limit of drinking water except Alanga wetland. However, As levels were higher than that recommended for livestock water quality levels. Eighty-seven percent of the investigated wetlands showed lower content of Pb than WHO recommended permissible limit of drinking water, but two wetland waters (Dohuria-1 and Chowdhuri) were polluted with higher Pb levels. Sixty-seven percent of the investigated wetlands displayed higher levels of Cd than WHO recommended permissible limit in drinking water. Dissolved organic material showed no significant difference among the 15 investigated wetlands water, but total dissolved solids was significantly greater. The condition of the water of all wetlands was basic pH. All water samples were applied to linear regression equation and correlation coefficients where values showed no significant differences. Data demonstrate that the estimated high metal concentrations of these ponds may contribute to bioaccumulation within plants, food grains and shrimp.     

A study on the accumulation of nine heavy metals in some important fish species from a natural reservoir in Riyadh,Saudi Arabia

Concentrations of nine heavy metals (Cr, Cd, Pb, Ni, Cu, Zn, Mn, As, and Fe) in the muscles of four fish species (O. niloticus, C. gariepinus, P. latipinna, and A. d. dispar) collected from the Riyadh River were detected using atomic absorption spectrophotometry in two different seasons in 2012. The concentrations of the studied heavy metals except Cd, Pb, Ni, and Cu in Aphanius d. dispar and Poecilia latipinna were found to be below the safe limits suggested by various authorities. This study also showed that Zn was predominant, while Cr was least accumulated metal in the studied fish muscles. Data demonstrated that there was a significant variation in the heavy-metal concentrations in different fish species in the Riyadh River. Significant positive correlations between heavy-metal concentrations in fish muscles were also found both in pre- and post-monsoon seasons. Metal pollution index was calculated to distinguish polluted from unpolluted ecosystems based upon current knowledge of metal bioavailability, bioconcentration, and bioaccumulation patterns. From the human health point of view, this study showed that there was a possible health risk to consumers due to the intake of Aphanius d. dispar and Poecilia latipinna under the current consumption rate in the country.     

Biomarkers of oxidative stress as indicators of water pollution in Nile tilapia (Oreochromis niloticus) from a water reservoir in Riyadh,Saudi Arabia

Antioxidant enzyme activities of fish (Oreochromis niloticus) were determined in order to assess the status of pollution in the Wadi Namar (WN), near Riyadh, Saudi Arabia. Activities of four antioxidant enzymes as superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and concentrations of glutathione (GSH) and oxidant malondialdehyde (MDA) were selected as bioindicators. Fish (n = 14) were sampled in the month of April 2013 from WN and a control site (CS). SOD activity was increased by 37.9%, 47%, and 29% in kidney, liver, and heart, respectively, while a significant decrease (36.4%) was observed in gills of O. niloticus from WN as compared to fish from CS. CAT activity was reduced by 51%, 55%, 47%, and 35% in kidney, liver, heart, and gills of O. niloticus from WN. The GST activities in kidney, liver, and heart of O. niloticus from WN were elevated by 34%, 48%, and 32%, respectively. However, significant fall (49%) in gills of fish was noted from WN compared to fish from CS. GSH levels were increased by 44%, 36%, and 38% in kidney, liver, and heart, respectively, but decreased by 30% in gills. MDA levels of O. niloticus were significantly increased in kidney, liver, and heart in fish from WN. Data indicated that WN is polluted mainly by industrial and urban discharge of liquid waste products.     

Study of atrazine degradation in soil from Kenyan sugarcane-cultivated fields in controlled laboratory conditions

A study to compare the extent of atrazine mineralization in soils from Kenyan sugarcane-cultivated fields with and without history of atrazine use was carried out in the laboratory under controlled conditions. The study was testing the hypothesis that repeated atrazine application to soil will not result in enhanced atrazine mineralization. The study was carried out with ¹⁴C-uniformly ring-labeled atrazine in a laboratory under controlled conditions. Atrazine mineralization to ¹⁴CO₂ in soil with no history of atrazine use was negligible (0.16%) after 163 days of soil incubation. The three metabolites hydroxyatrazine, desisopropylatrazine, and desethylatrazine in the proportion of 17.7%, 1.3%, and 2.6%, respectively, were in the soil after 75 days. In the soil from the sugarcane-cultivated field with history of atrazine use, atrazine mineralization was 89.9% after 98 days. The same soil, amended with mature compost, showed a lag phase of eight days before rapid atrazine mineralization was observed.